The general objective of the present invention is to improve on that class of vacuum test fixture shown in U.S. Pat. No. 4,344,033, issued Aug. 10, 1982, to Stowers et al.
More particularly, it is an object of the present invention to provide a modular vacuum fixture of greater simplicity and compactness, reduced weight and greatly increased convenience of use and versatility.
Another object of the invention is to provide a modular vacuum test fixture for loaded PCBs in which key components of the fixture are formed from state-of-the-art molded structural plastics with precision and without sacrificing strength and durability. Similarly, in accordance with the invention, the top plate and lower pin plate of the test fixture are formed from a laminated glass epoxy resin, selected because of its outstanding dielectric characteristics and machinability. In the prior art, these components were formed of a phenolic compound, or the like, and were very difficult to drill with precision, and required greater thickness in their fabrication to achieve stability and consequently were much heavier than the critical top and bottom laminated epoxy glass resin plates employed in the present invention. For example, the bottom plate in the present invention need be no thicker than 3/8th inch. Point drilling is made easier and more accurate in the thinner material. Somewhat increased material costs are partially offset by reductions in machining costs and production time. The new material for the top and bottom plates of the fixture enables a very accurate dense drilling pattern of up to 0.040 inches between centers.
Another object of the invention is to provide a more economical and more effective gasket applied removably to the margin of the top plate of the fixture without adhesive and having a yielding skirt portion capable of forming an air-tight seal with an underlying lower plate retainer or frame formed of injection molded high strength plastics material, preferably ABS "CYCOLAC".
A further important object of the invention is to provide a vacuum test fixture of the above-mentioned type which can be snapped together as an assembly and separated into its components by hand without tools. In the assembly, manual thumb screws are employed to retain the bottom plate carrying the electrical contact pins or probes removably assembled with the bottom plate retainer or frame, the entire structure being characterized by simplicity and greatly increased convenience of use.
Other features and advantages of the invention will become apparent to those skilled in the art during the course of the following detailed description.